1. Field of the Invention
The invention relates to a knee prosthesis. More precisely, it relates to a knee prosthesis of the type comprising a tibial plateau anchored at the upper end of the tibia, the tibial plateau having an attached insert which is intended to cooperate with a femoral component anchored in the lower end of the femur.
2. Description of Background and Relevant Information
It is known that the insert, in most cases made of polyethylene, is subjected to repeated stresses exerted simultaneously by the tibial plateau and the femoral component during the movement of extension or flexion of the femur on the tibia, or vice versa, the permanent stresses leading to progressive wear and tear of the polyethylene.
To solve this problem, the document FR-A-2 735 017 has proposed a prosthesis, of the type in the present invention, comprising a median pin projecting from the upper face of the tibial element, the pin being engaged in a corresponding cavity formed on the lower face of the insert, and this in combination with arrangements in the form of lateral studs formed on the upper part of the tibial plateau and able to slide along two corresponding lateral cuttings provided on the lower face of the insert.
Although this configuration permits rotation of the femoral component on the tibial plateau during flexion of the knee, the insert nevertheless does not reproduce simultaneously the natural movement of the meniscus in the posteroanterior sense.
Likewise, the insert does not reproduce the movement of the meniscus on the tibial plateau during extension of the knee, namely a translation of the meniscus in the anteroposterior sense, then rotational blocking of the meniscus.
In order to reproduce the natural knee joint, the document WO 96/38103 has proposed a prosthesis in which the tibial plateau has two projecting studs, respectively anterior and posterior, which are intended to cooperate respectively with two indentations formed on the lower face of the intermediate component or insert.
The prosthesis proposed in this document, by virtue of the shape of the indentations, permits an at one and the same time lateromedial, anteroposterior and rotational movement of the insert on the tibial plateau. It nevertheless has a number of disadvantages to the extent that the rotation of the insert during flexion of the knee is effected on a vertical axis passing through the posterior stud of the tibial plateau. In other words, it is not possible here to reproduce the natural movement of the knee joint in flexion, according to which the rotation of the meniscus on the tibial plateau is effected on a substantially central axis.
Moreover, and as before, the arrangements provided in the area of the tibial plateau and of the insert do not permit rotational blocking of the insert during extension of the knee.